This invention relates to auxiliary lighting systems for use with high intensity discharge (HID) lamps and more particularly to provision of auxiliary lighting when the HID lamp is first turned on and when the HID lamp turns off due to power interrupt. These two conditions are known as cold start and hot interrupt.
The need for an auxiliary lamp and some of the background of the operation of these HID lamps is set forth in U. S. Pat. No. 4,005,331 issued Jan. 25, 1977 and entitled "High Intensity Discharge Lamp With Auxiliary Light".
High intensity discharge (HID) lamps have the great advantage of being energy efficient. High pressure sodium and metal halide lamps for example provide both high light levels and good color characteristics. The operation of many types of HID lamps requires the addition of ignitors to the ballast circuit in order to enable the arc to be struck. Conventional ballasts and solid state ballasts have been designed for use with HID lamps. Even with the inclusion of ignitors, there is still a period of time during initial start-up when the light output from the HID lamp is insufficient to enable safe entry into areas illuminated by these devices. This is called cold start. A period of several minutes may elapse before these lamps achieve their full light output.
Additionally, despite the inclusion of ignitors which generate high voltages to establish the arc within the HID lamp, if there is a momentary interruption in the power source, the lamp will not re-establish its arc for a period of time ranging from a minute to several minutes. This is called hot interrupt. During this time, as well as during normal start-up, it is desirable to provide auxiliary light.
When conventional ballasts are employed for HID lamps, it is common to place a relay which has a current sensing coil in the ballast secondary, in series with the HID lamp. A set of normally closed contacts is placed in series with an incandescent lamp and an AC power source. When the arc is established in the HID lamp, current flows through the current sensing coil and the normally closed contacts are driven open thereby extinguishing the auxiliary light. A device of this type provides auxiliary light only during times of hot interrupt. During hot interrupt, the HID lamp is too hot to enable the ignitor to re-establish an arc. As soon as the arc is re-established, the current flow to the HID lamp causes the current coil of the normally closed relay to drive the contacts open thereby switching the incandescent lamp off.
If auxiliary light during cold start is desired, i.e. when a cool HID is to be energized, additional components must be added. In view of the fact that the ignitor delivers pulses up to several thousand volts to the HID lamp, it is impractical to place voltage sensing coils across the HID lamp in order to sense normal operating parameters and open circuit conditions. The placement of such a voltage sensing coil is common with mercury vapor and conventional metal halide lamps which do not have ignitors. For HID systems which incorporate ignitors, the general means of providing auxiliary lighting during cold start is to employ a current sensing relay with normally open contacts in series with the ballast output and the HID lamp. The normally open contacts of this relay close when current flows to the HID lamp and, in turn, control a normally closed timing device which turns off the auxiliary incandescent lamp after a pre-determined time period.
Solid state ballasts which incorporate the ignitor function have been developed for HID lamps. They offer advantages of cooler operation, less power loss and quieter operation. The use of a solid state ballast and ignitor creates difficult operating conditions for auxiliary lighting controls. The high voltage ignitor pulses which they generate require wire with special insulation characteristics which precludes the use of a conventional current sensing relay in series with the ballast output and the HID lamp. A typical ballast system of this type was developed by General Electric Company. Their 32 watt metal halide lamp that provides a light output similar to a 150 watt incandescent. The solid state ballast HID lamp combination uses a total of only 37.5 watts. The system provides 66.6 lumens/watt (over 3 times the 150 watt incandescent). The ignitor voltage and wire insulation requirements of the ballast precludes its use with conventional HID auxiliary lighting controls.
Accordingly, it is a major purpose of this invention to provide an auxiliary lighting system that can be employed with HID lamps having a solid state ballast and ignitor.
More particularly, the purpose of this invention is to provide a simple auxiliary lighting system with a minimum number of components, which is relatively inexpensive and can be employed with a wide range of HID lamps having a solid state ballast.